This application is based upon application No. 2000-42137 filed in Japan on Feb. 21, 2000, the contents of which are hereby incorporated by reference.
1) Technical field of the Invention
The present invention relates to an image reader for reading an image on an original document for use with an image reproducing device such as a copy machine, a printer, a facsimile machine and a scanner. In particular, the present invention relates to an image reader for reading the image on the original document through a transparent substrate such as platen glass, while the original document is being transported on and along the transparent substrate.
2) Description of Related Arts
The conventional image readers are categorized into two types according to an image reading methods. One type of image reader includes a movable image reading element moving back and forth behind a transparent substrate or platen on which an original document is transported to a predetermined reading region. The document is maintained in the reading region while the movable reading element moves across the document to read its image. The first type of image reader incorporating the movable image reading element is referred to as xe2x80x9cmovable image readerxe2x80x9d hereinafter as required. The other type of the image reader includes a stationary image reading element behind the transparent substrate, in which the original document is transported on the transparent substrate while the stationary image reading element reads the image of the original document. The second type of the image reader incorporating the stationary image reading element is referred to as xe2x80x9cstationary image readerxe2x80x9d hereinafter as required.
The movable and stationary image readers have respective advantages and disadvantages. For example, a spot on the transparent substrate is reproduced on a resultant image in different ways. Specifically, according to the movable image reader, since the original document is fixed to the transparent substrate, the spot on the substrate is reproduced as it is on the resultant image. Therefore, the spot, if it is so small, hardly deteriorates the resultant image quality. Contrary to this, according to the stationary image reader, since the original document is moved relative to the substrate, even the small spot on the substrate is reproduced into an unwanted line extending along the scanning direction, causing a harmful deterioration in the resultant image.
For this reason, the transparent substrate of the stationary image reader has a surface covered by a protection layer in order to prevent the creation of permanent spot on the substrate. Unfortunately, the repetition of the frictional contact with the documents wears the protection layer, which causes the transparent substrate to be spotted and thereby creates the unwanted lines on the resultant images.
To prevent this, the transparent substrate should be exchanged by a new one after the formation of the unwanted lines. However, the transparent substrate is so expensive that a frequent exchange of the transparent substrate increases the cost for reading. Accordingly, a demand has been existed to develop a image reader or image reproducing device, in which the transparent substrate can be available for an extended lifetime.
Accordingly, a first object of the present invention is to provide an improved transparent substrate of a stationary image reader, which can be used effectively for an extended lifetime.
A second object of the present invention is to provide the improved transparent substrate having a protection layer which is less wearable but also harmless against a smooth reading of the original document.
To achieve the aforementioned first object of the present invention, an image reader according to the first aspect, comprises a transparent substrate having a first surface and a second surface opposing to the first surface, at least one of the surfaces having a protection layer; a document transporting device for transporting a document along the first surface of the transparent substrate; and an image pickup device positioned adjacent to the second surface and for picking up an image of the document transported along the first surface of the transparent substrate; wherein the transparent substrate can be turned around relative to the image pickup device, wherein the transparent substrate has a first indicator showing how the transparent substrate has been turned around relative to the image pickup device. Thus, even after a region of the protection layer of the transparent substrate has been worn out, since the transparent substrate can be turned around relative to the image pickup, the image reader can read the original document through another active region of the protection layer. Therefore, the transparent substrate can be effectively used for an extended time period before replacing with a new one.
To achieve the aforementioned second object of the present invention, an image reader according to the second aspect, comprises a transparent substrate having a first surface and a second surface opposing to the first surface, the first surface having a protection layer; a document transporting device for transporting a document along the first surface of the transparent substrate; and an image pickup device positioned adjacent to the second surface and for picking up an image of the document transported along the first surface of the transparent substrate; wherein the protection layer contains a silicone oil and a compound with per-fluoro-alkyl group. Thus, the silicone oil allows the protection layer to endure the active friction generated during repeatedly transporting original documents, resulting in delaying the abrasion thereof, and the per-fluoro-alkyl group containing compound keeps the blur and/or the dust away from the protection layer.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the sprit and scope of the invention will become apparent to those skilled in the art from this detailed description.